diff options
Diffstat (limited to 'arch/x86/kernel/alternative.c')
| -rw-r--r-- | arch/x86/kernel/alternative.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index cdc43242da92..318a4f9b7ece 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -273,6 +273,7 @@ struct smp_alt_module { }; static LIST_HEAD(smp_alt_modules); static DEFINE_SPINLOCK(smp_alt); +static int smp_mode = 1; /* protected by smp_alt */ void alternatives_smp_module_add(struct module *mod, char *name, void *locks, void *locks_end, @@ -354,7 +355,14 @@ void alternatives_smp_switch(int smp) BUG_ON(!smp && (num_online_cpus() > 1)); spin_lock_irqsave(&smp_alt, flags); - if (smp) { + + /* + * Avoid unnecessary switches because it forces JIT based VMs to + * throw away all cached translations, which can be quite costly. + */ + if (smp == smp_mode) { + /* nothing */ + } else if (smp) { printk(KERN_INFO "SMP alternatives: switching to SMP code\n"); clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP); @@ -369,6 +377,7 @@ void alternatives_smp_switch(int smp) alternatives_smp_unlock(mod->locks, mod->locks_end, mod->text, mod->text_end); } + smp_mode = smp; spin_unlock_irqrestore(&smp_alt, flags); } @@ -441,7 +450,10 @@ void __init alternative_instructions(void) alternatives_smp_module_add(NULL, "core kernel", __smp_locks, __smp_locks_end, _text, _etext); - alternatives_smp_switch(0); + + /* Only switch to UP mode if we don't immediately boot others */ + if (num_possible_cpus() == 1 || setup_max_cpus <= 1) + alternatives_smp_switch(0); } #endif apply_paravirt(__parainstructions, __parainstructions_end); |